An optical communication technique using an optical fiber as a transmission medium has brought in an increase on a transmission distance of a signal, thus building a large scale of an optical communication network. Recently along with wide spread of the Internet communications, communication traffic abruptly increases, thus increasing demands for large capacity, high bitrate and high functionality of the communication network. Until now, introduction of a multiple-wavelength communication technique for simultaneously transmitting a plurality of optical signals having different wavelengths by a single transmission route enables the transmission capacity between two points to be increased.
In the communication network, however, it is necessary to route or switch routes of signals in a node where a plurality of transmission paths combine, and along with an increase in transmission capacity, signal processing thereof has become a bottleneck. Until now, there is adopted a method in which the transmitted optical signal is once converted into an electrical signal, thereafter the route routing or route switching is performed, and the electrical signal is again converted into an optical signal, which is sent to a transmission path. From now on, it is expected that a method for executing the routing or switching processing of the signal route without converting the optical signal into the electrical signal can be adopted to significantly increase throughput of the node. An optical switch is a component absolutely necessary for introducing such a method to the optical communication network.
The optical switch is configured to connect a plurality of unit optical switch elements each having one input and two outputs or two inputs and one output, thereby making it possible to produce optical switches of various kinds of circuit configurations in regard to input/output port numbers or connecting patterns between ports, such as multiple connections of one input and multiple outputs (or multiple inputs and one output), multiple inputs and multiple outputs or two inputs and two output. Among them, a matrix optical switch of multiple inputs and multiple outputs is widely used as an optical switch for arbitrarily routing direction routes between a plurality of input and output ports.
Further, there is a demand for a matrix optical switch in which not only a regular connection of one input to one output but also a connection from “multiple inputs to one output” to “one input to multiple outputs” is made possible. That is, the matrix optical switch, which has a connecting function of multiple inputs to one output in which different optical signals that are input to a plurality of input ports combine, which is output to one output port among a plurality of output ports or a connecting function of one input to multiple outputs in which an optical signal that is input to one input port among a plurality of input ports is branched, which are output to a plurality of output ports, is required for building a flexible network.
There is known a configuration as shown in FIG. 1 as the configuration of a waveguide type optical switch in which the matrix optical switch having this connecting function from “multiple inputs to one output” to “one input to multiple outputs” is realized by a waveguide type device (refer to Non-Patent Literature 1).
The matrix optical switch shown in FIG. 1 comprises four optical switches 111 to 114 each having one input and four outputs (combination of four unit optical switch elements each having one input and two outputs), and four optical combining devices 131 to 134 each having four inputs and one output. The respective inputs in the optical switches 111 to 114 are connected to four external input ports 101 to 104. The respective outputs in the optical combining devices 131 to 134 are connected to external output ports 141 to 144.
The four output ports of the optical switch 111 are respectively connected to the input ports of the optical combining devices 131 to 134 via an intersection part 121. Similarly the four output ports of each of the optical switches 112 to 114 are respectively connected to the input ports of the optical combining devices 131 to 134 via the intersection part 121.
According to this configuration, the different optical signals that are input to the plurality of external input ports can combine to be output to one external output port.
In a case where the external input port and the external output port in the optical switch shown in FIG. 1 are reversed and the optical combining device is thus used as the optical branching device as it is, an optical signal that is input to one external input port can be branched to be output to a plurality of external output ports.